The invention relates to a device for automatically controlling a high-lift system of an aircraft.
Document US 2006/049308 A1 describes an aircraft wing system with lift devices and a drive system with a drive link coupleable to the lift devices and a control system coupled to the drive system. The control system has a first configuration for which the drive link is operatively coupled to a fist and a second deployable lift devices, wherein activation of at least a portion of the drive link moves the fist and second deployable lift device. The control system further has a second configuration for which the drive link is operatively coupled to the first deployable lift device and operatively decoupled from the second deployable lift device, wherein on activation of at least a portion of the drive link the first deployable lift device moves relative to the second deployable lift device.
A multitude of high-lift systems that are used to increase maximum lift on the wing of aircraft during takeoff, landing and slow flight are known. These are used in civil commercial aircraft and in other transport aircraft as well as in business aircraft and motorised sports aircraft. In the case of civil commercial aircraft and other transport aircraft, high-lift systems with wing leading-edge flaps and wing trailing-edge flaps have become widespread as aerodynamically effective high-lift elements. Wing leading-edge flaps are designed with or without a gap between the flap and the main wing, while trailing-edge flaps are usually designed as single-gap or multiple-gap trailing-edge flaps.
As a rule, activation of such flaps or high-lift elements presently takes place manually by way of an operating lever in the cockpit, wherein in a flap control unit electrical signals are generated that correspond to the lever position, which signals control the flap position by means of electrical or hydraulic actuators. Normally, the flaps or high-lift elements are extended for takeoff, holding flight and landing, while they are retracted for cruising so as to reduce aerodynamic resistance or drag. Since in relation to flight performance and noise generation different deflection angles are optimal for takeoff, landing and, if applicable, holding flight, various positions can be selected.
Furthermore, there are concepts for automatically extending leading-edge high-lift devices as a protective measure when a critical angle of attack is exceeded, or when the flight speed drops below a predetermined limit so that stalling and the associated loss of lift are prevented. Moreover, there are systems which by means of retraction are designed to prevent structural overload of the leading-edge flaps or the trailing-edge flaps when an upper predetermined limit flight speed is exceeded.
In addition, concepts are known that aim to automate the control of high-lift systems. In these concepts a differentiation can be made between those that are intended to optimise flight performance, which is in particular relevant to takeoff, and those which are primarily intended to protect the aircraft from any damage or from the occurrence of uncontrolled flight states.
From U.S. Pat. No. 2,350,751 a system is known in which both control and extension and retraction of trailing-edge flaps are carried out electrically by means of a motor. Flap control is to be controlled in such a manner that maximum lift of the aircraft wing is increased. A flap lever makes it possible to manually select among three different deflection angles, namely one in which the deflection angle is zero (hereinafter also referred to as “retracted state” or “cruising position”), one for takeoff, and one for landing. The known system is designed for automatically retracting the flaps after takeoff when a certain dynamic pressure is exceeded. According to a flap lever position that is selected in flight by way of the flap lever, the flaps automatically extend to the corresponding takeoff or landing position if the dynamic pressure drops below a threshold value that is independent of the selected configuration.
The system makes it possible, in the case of dynamic pressures below the dynamic-pressure threshold value, to select any of the three flap positions by way of the flap lever, wherein the selected configurations are assumed immediately. Above the threshold value, independently of the position of the flap lever, a transition to the retracted position is always initiated.
Disadvantageously, the known system provides only for a single switching dynamic pressure. Due to aerodynamic, structural/mechanical and flight-performance-related boundary conditions of high-lift systems of large modern aircraft, suitable speeds for resetting the flaps from the takeoff position to the cruising position vary greatly in relation to the speed of extending the flaps from the cruising position to the landing approach position. The usual manually-operated flap systems of these aircraft take account of the adjacent discrete flap deflection angles, i.e. flap positions, by means of a cascade of overlapping speed ranges. The change of the flap configuration from the cruising position to the landing position takes place incrementally in intermediate steps. In order to obtain adequate speed overlap in a large commercial aircraft, more than merely two or three different positions for the high-lift flaps are required if at the same time the maximum operating speeds in the individual configurations are limited. For example, the Airbus A320 provides six different positions (0, 1, 1+F, 2, 3, Full). Limiting the maximum operating speed is used to prevent the occurrence of flight states in which inadmissibly high structural loads can act on the high-lift flaps. By limiting the operating speeds, the expected loads are reduced, and consequently, with corresponding dimensioning, the structural weight can be limited to an extent that is optimal in the context of the overall concept.
DE 25 31 799 C3 describes a speed-dependent automatic flap switching device, that comprises largely automatic flap control. It is the objective to prevent the occurrence of accidents resulting from the aircraft's crew failing to set the flaps. In contrast to the previously-mentioned known device, in this design only two flap positions are provided instead of three. In contrast to this, a speed hysteresis continues to be provided, which in flight results in the flaps being retracted at a higher flight speed, and being extended again at a comparatively lower flight speed only if the switch configuration of a dynamic-pressure switch provided in this known automatic flap switching device is not changed. If the dynamic pressure is in a range that is significantly greater than zero, but less than required for liftoff, a contact of the dynamic-pressure switch is closed, which supplies current to the electrical flap drive in the direction of retraction. If the dynamic pressure increases, this current circuit is interrupted. In the higher pressure range that follows the interruption range, which higher pressure range begins below a dynamic pressure required for liftoff, and ends at values that are typical for the initial steep climb, another contact is closed, and as a result of this the flap drive motor is supplied with current in the direction of extension of the flaps. In another embodiment of this known automatic switching device, the current circuit for extending the flaps is closed already at the time of taxiing by way of a switch that is coupled to the rotational speed of the running gear wheels. During further increase to a dynamic pressure that is typical for cruising, the closure of a third contact again results in the flaps being retracted. Between the individual dynamic pressure ranges there are zones in which none of the current circuits is closed. With renewed successive reduction in the dynamic pressure, the above-described sequence takes place in reverse. Thus in the case of very low and very high flight speeds, corresponding to the dynamic pressures that are present, the flap is moved to the retracted state, while in the case of medium dynamic pressures that are typical for liftoff of the aircraft, for initial steep climb as well as for the approach to landing, and for landing, the flap is extended or left in the extended state. According to the known solution it is optionally also possible to manually extend the flaps before takeoff. An open interrupter switch then prevents retraction of the flaps during the takeoff taxiing procedure. The known automatic flap switching device is associated with a disadvantage in that only the selection of one of two flap positions (namely the retracted or the extended position) is possible. There is a further disadvantage in that while the dynamic switching pressures can be modified by displacement of the sliding contacts of the dynamic-pressure switch, this does however require pilot intervention. Depending on the mass of the aircraft at the time, in each case the switching speeds need to be set prior to takeoff and prior to landing, in order to cause retraction or extension of the flaps at suitable speeds.
U.S. Pat. No. 4,042,197 describes a further automatic high-lift system for takeoff and landing of an aircraft, with the difference of the control of both flight phases differing significantly in each flight phase. It is the objective to reduce aircraft noise emissions on the ground during takeoff and landing. As a result of the automatic device, during takeoff earlier retraction of the flaps after liftoff is to take place when compared to conventional manual operation, and consequently the aerodynamic resistance is to be reduced while the climb rate is to be increased early. During the approach, the automatic device is to make it possible for the aircraft to be brought to the landing configuration later than is customary with manual selection of the flap position by a pilot.
In the known automatic device the flaps are manually extended, prior to takeoff, by operating a flap lever. Subsequently the flap lever is moved to the position up to which the automatic device is to retract the flaps automatically after takeoff. No further explanations relating to the necessary switching logic are provided. Automatic retraction of the flaps after takeoff takes place depending on the flight speed after retraction of the running gear. The speed at which retraction of the flaps commences is preselected by the cockpit crew prior to takeoff. Longitudinal acceleration of the aircraft is integrated twice in order to determine the distance from commencement of the takeoff taxiing procedure. When a preselected distance has been reached, a cockpit display indicates to the crew the point for reducing engine thrust. Apart from a reduction in the thrust, the pitch angle of the aircraft is reduced to such an extent that the aircraft at a significantly reduced climb rate accelerates despite the reduced propulsion, thus finally reaching the switching speed for retracting the flaps.
In this known automatic high-lift system in the approach phase it is provided for the flaps to be extended depending on the distance to the (desired) touchdown point or on the continuously measured altitude. In the first case the distance information is provided either by an inertial navigation system or by way of evaluating a DME-signal. In the second case the barometric altitude is used, which is explicitly preferred to the radio altitude. Both the operating mode and the distance or the altitude at which the landing configuration is to be attained is specified by the cockpit crew by way of an operating unit. The known system provides for an approach to landing with continuous deceleration, during which approach the flaps are also continuously moved from the retracted position to the landing position. Both the engine thrust and the setting angle of a trimmable elevator tail plane are adjusted to the respective flap position by way of the pre-control functions. The speed instruction for the propulsion regulating device is adjusted depending on the flap position. In a final approach speed entered by the pilot, by way of the operating device, as the lower limit, the landing flap configuration is finally attained.
This known automatic high-lift system is associated with a disadvantage in that prior to the approach the pilots need to manually state which signals are to be used to control the automatic device for the high-lift flaps. Manual specification of flight guidance parameters (speed, distance, altitude) by pilots not only increases their workload but is also associated with the danger of incorrect entry. There is no go-around logic circuit provided for cases in which the landing approach is aborted in favour of go-around, and consequently a manual operating device parallel to the described automatic device is required.
Finally, apart from a function that supports the pilot or pilots, which function comprises a signal for displaying the extension of the high-lift flaps at an optimum point in the approach trajectory, EP 1 684 144 A1 proposes as an alternative the use of said supporting signal for automatic extension of the high-lift flaps. It is stated that the automatic function is preferably to be implemented in a flight management system. To this effect a navigation system is used that is based on the preplanning of the lateral and vertical flight path profiles. Switching conditions for the transition from one path section to another, and also for generating a signal that causes the high-lift flaps to be brought to a position that corresponds to pre-planning, are determined in the form of altitudes, flight speeds or lateral positions of the aircraft, or in the form of a combination of these parameters. If the state parameters that are necessary for switching reach or exceed the switching conditions, then the high-lift means are brought to the position allocated according to planning.
This functionality is associated with a disadvantage in that it can only be applied to the approach phase. Thus, automatic operation of the high-lift flaps is not provided for during flight preparation, taxiing on the ground, takeoff, climbing flight and cruising, go-around after an aborted approach, during landing, and during operation on the ground after landing. Furthermore, for guiding the aircraft along the pre-planned flight path, corresponding navigation information is mandatory. If this information is not available, the navigation system does not work, and thus the functionality for automatically extending the high-lift flaps is not available.